void main(List<String> args) {
  Person p = Person('张三', 18);
  p.sleep();
  p.run();
  p.eat();
}

class Person {
  String? name;
  int? age;
  Person(this.name, this.age);
  void run() {
    print('run');
  }

  void eat() {
    print('eat');
  }

  void sleep() {
    print('$name, $age');
  }
}
